Flexible sensors and sensor systems

ABSTRACT

Sensor systems are described that are designed to be integrated with gloves for the human hand. An array of sensors detects forces associated with action of a hand in the glove, and associated circuitry generates corresponding control information that may be used to control a wide variety of processes and devices.

RELATED APPLICATION DATA

The present application is a continuation of and claims priority under35 U.S.C. 120 to U.S. patent application Ser. No. 15/621,935 entitledSensor System Integrated with a Glove filed on Jun. 13, 2017 (AttorneyDocket No. BBOPP007X1), which is a continuation-in-part of and claimspriority under 35 U.S.C. 120 to U.S. patent application Ser. No.14/928,058 entitled Sensor System Integrated with a Glove filed on Oct.30, 2015 (Attorney Docket No. BBOPP007), which is a non-provisional ofand claims priority under 35 U.S.C. 119(e) to U.S. Provisional PatentApplication No. 62/072,798 entitled Flexible Sensors and Applicationsfiled on Oct. 30, 2014 (Attorney Docket No. BBOPP004P3). U.S. patentapplication Ser. No. 14/928,058 is also a continuation-in-part of andclaims priority under 35 U.S.C. 120 to U.S. patent application Ser. No.14/671,821 entitled Flexible Sensors and Applications filed on Mar. 27,2015 (Attorney Docket No. BBOPP004X2), which is a continuation-in-partof and claims priority under 35 U.S.C. 120 to U.S. patent applicationSer. No. 14/299,976 entitled Piezoresistive Sensors and Applicationsfiled Jun. 9, 2014 (Attorney Docket No. BBOPP004). The entire disclosureof each of the foregoing applications is incorporated herein byreference for all purposes.

BACKGROUND

Demand is rapidly rising for technologies that bridge the gap betweencomputing devices and the physical world. These interfaces typicallyrequire some form of sensor technology that translates information fromthe physical domain to the digital domain. The “Internet of Things”contemplates the use of sensors in a virtually limitless range ofapplications, for many of which conventional sensor technology is notwell suited.

SUMMARY

According to various implementations, sensors and applications ofsensors are provided. According to some implementations, a sensor systemincludes a flexible substrate for alignment or integration with aportion of a glove. A plurality of conductive trace groups formeddirectly on the substrate at sensor locations correspond to at leastsome finger joints of a human hand. Each of the conductive trace groupsincludes two or more conductive traces. The resistance between theconductive traces in each of the conductive trace groups varies withforce on piezoresistive material in contact with the conductive tracegroup. Circuitry is configured to receive a signal from each of theconductive trace groups and generate control information in responsethereto. The control information represents the force on thepiezoresistive material in contact with each of the conductive tracegroups.

According to a particular class of implementations, the flexiblesubstrate is a dielectric material, and the piezoresistive material is aplurality of patches. Each patch of piezoresistive material is incontact with a corresponding one of the conductive trace groups at thesensor locations. According to a more specific implementation, thedielectric material is a thermoplastic material, and the sensor systemincludes a second flexible substrate of the thermoplastic material. Theflexible substrate on which the conductive trace groups are formed, thepatches of piezoresistive material, and the second flexible substrateare thermally bonded together such that the patches of piezoresistivematerial are secured in contact with the corresponding conductive tracegroups.

According to another class of implementations, the flexible substrate isthe piezoresistive material which may be, for example, a piezoresistivefabric.

A further understanding of the nature and advantages of variousimplementations may be realized by reference to the remaining portionsof the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows examples of trace patterns that may be integrated with aflexible substrate.

FIG. 2 shows examples of different types of distortions to a flexiblesubstrate.

FIG. 3 shows a particular implementation of a sensor array.

FIG. 4 is a simplified block diagram of sensor circuitry suitable foruse with various implementations.

FIG. 5 shows examples of relationships among a piezoresistive substrate,conductive traces, and other conductive elements in one-sided andtwo-sided sensor implementations.

FIG. 6 shows another implementation of a sensor array.

FIG. 7 shows another implementation of a sensor array.

FIG. 8 shows an example of a cross-section of some of the components ofa sensor system.

FIG. 9 shows an example of a sensor array integrated with a glove blank.

FIG. 10 shows another implementation of a sensor array.

FIG. 11 shows another implementation of a sensor array.

FIGS. 12-14C show another implementation of a sensor system.

FIGS. 15 and 16 show another implementation of a sensor system.

DETAILED DESCRIPTION

Sensors and sensor systems incorporating piezoresistive materials aredescribed in this disclosure. In particular, sensor systems forintegration with gloves for the human hand are described. Specificimplementations are described herein including the best modescontemplated. Examples of these implementations are illustrated in theaccompanying drawings. However, the scope of this disclosure is notlimited to the described implementations. Rather, this disclosure isintended to cover alternatives, modifications, and equivalents of theseimplementations. In the following description, specific details are setforth in order to provide a thorough understanding of the describedimplementations. Some implementations may be practiced without some orall of these specific details. In addition, well known features may nothave been described in detail to promote clarity.

Piezoresistive materials include any of a class of materials thatexhibit a change in electrical resistance in response to mechanicalforce or pressure applied to the material. One class of sensor systemsdescribed herein includes conductive traces formed directly on orotherwise integrated with a flexible substrate of piezoresistivematerial, e.g., a piezoresistive fabric or other flexible material.Another class of sensor systems described herein includes conductivetraces formed directly on or otherwise integrated with a flexibledielectric substrate with flexible piezoresistive material that istightly integrated with the dielectric substrate and in contact withportions of the traces. When force or pressure is applied to such asensor system, the resistance between traces connected by thepiezoresistive material changes in a time-varying manner that isrepresentative of the applied force. A signal representative of themagnitude of the applied force is generated based on the change inresistance. This signal is captured via the conductive traces (e.g., asa voltage or a current), digitized (e.g., via an analog-to-digitalconverter), processed (e.g., by an associated processor, controller, orsuitable control circuitry), and mapped (e.g., by the associatedprocessor, controller, or control circuitry) to a control function thatmay be used in conjunction with virtually any type of process, device,or system. The output signals from such sensor systems may also be usedto detect a variety of distortions and/or deformations of thesubstrate(s) on which they are formed or with which they are integratedsuch as, for example, bends, stretches, torsions, rotations, etc.

Printing, screening, depositing, or otherwise forming conductive tracesdirectly onto flexible substrates allows for the creation of a sensor orsensor array that fits any arbitrary shape or volume. The piezoresistivematerial on which the traces are formed or with which the traces are incontact may be any of a variety of woven and non-woven fabrics havingpiezoresistive properties. Implementations are also contemplated inwhich the piezoresistive material may be any of a variety of flexible,stretchable, or otherwise deformable materials (e.g., rubber, or astretchable fabric such as spandex or open mesh fabrics) havingpiezoresistive properties. The conductive traces may be formed on thepiezoresistive material or a flexible dielectric substrate using any ofa variety of conductive inks or paints. Implementations are alsocontemplated in which the conductive traces are formed using anyflexible conductive material that may be formed on a flexible substrate.It should therefore be understood that, while specific implementationsare described with reference to specific materials and techniques, thescope of this disclosure is not so limited.

Both one-sided and two-side implementations are contemplated, e.g.,conductive traces can be printed on one or both sides of flexiblesubstrate. As will be understood, two-sided implementations may requiresome mechanism for connecting conductive traces on one side of thesubstrate to those on the other side. Some implementations use vias inwhich conductive ink or paint is flowed through the vias to establishthe connections. Alternatively, metal vias or rivets may makeconnections through the flexible substrate.

Both single and double-sided implementations may use insulatingmaterials formed over conductive traces. This allows for the stacking orlayering of conductive traces and signal lines, e.g., to allow therouting of signal line to isolated structures in a manner analogous tothe different layers of a printed circuit board.

Routing of signals on and off the flexible substrate may be achieved ina variety of ways. A particular class of implementations useselastomeric connectors (e.g., ZEBRA® connectors) which alternateconductive and non-conductive rubber at a density typically an order ofmagnitude greater than the width of the conductive traces to which theyconnect (e.g., at the edge of the substrate). Alternatively, a circuitboard (possibly made of a flexible material such as Kapton), or a bundleof conductors may be riveted to the substrate. The use of rivets mayalso provide mechanical reinforcement to the connection.

Matching conductive traces or pads on both the flexible substrate and acircuit board can be made to face each. A layer of conductive adhesive(e.g., a conductive epoxy such as Masterbond EP79 from Masterbond, Inc.of Hackensack, N.J.) can be applied to one of the surfaces and thenmated to the other surface. The conductive traces or pads can also beheld together with additional mechanical elements such as a plasticsonic weld or rivets. If conductive rivets are used to make theelectrical connections to the conductive traces of the flexiblesubstrate, the conductive adhesive may not be required. Conductivethreads may also be used to connect the conductive traces of theflexible substrate to an external assembly.

According to a particular class of implementations, the piezoresistivematerial is a pressure sensitive fabric manufactured by Eeonyx, Inc., ofPinole, Calif. The fabric includes conductive particles that arepolymerized to keep them suspended in the fabric. The base material is apolyester felt selected for uniformity in density and thickness as thispromotes greater uniformity in conductivity of the finishedpiezoresistive fabric. That is, the mechanical uniformity of the basematerial results in a more even distribution of conductive particleswhen the slurry containing the conductive particles is introduced. Thefabric may be woven. Alternatively, the fabric may be non-woven such as,for example, a calendared fabric e.g., fibers, bonded together bychemical, mechanical, heat or solvent treatment. For implementations inwhich conductive traces are formed on the piezoresistive fabric,calendared material presents a smoother outer surface which promotesmore accurate screening of conductive inks than a non-calendaredmaterial.

The conductive particles in the fabric may be any of a wide variety ofmaterials including, for example, silver, copper, gold, aluminum,carbon, etc. Some implementations may employ carbon graphenes that areformed to grip the fabric. Such materials may be fabricated usingtechniques described in U.S. Pat. No. 7,468,332 for ElectroconductiveWoven and Non-Woven Fabric issued on Dec. 23, 2008, the entiredisclosure of which is incorporated herein by reference for allpurposes. However, it should again be noted that any flexible materialthat exhibits a change in resistance or conductivity when force orpressure is applied to the material will be suitable for implementationof sensors as described herein.

According to a particular class of implementations, conductive traceshaving varying levels of conductivity are formed on flexiblepiezoresistive material or an adjacent flexible dielectric substrateusing conductive silicone-based inks manufactured by, for example, E.I.du Pont de Nemours and Company (DuPont) of Wilmington, Del., and/orCreative Materials of Ayer, Mass. An example of a conductive inksuitable for implementing highly conductive traces for use with variousimplementations is product number 125-19 from Creative Materials, aflexible, high temperature, electrically conductive ink. Examples ofconductive inks for implementing lower conductivity traces for use withvarious implementations are product numbers 7102 and 7105 from DuPont,both carbon conductive compositions. Examples of dielectric materialssuitable for implementing insulators for use with variousimplementations are product numbers 5018 and 5036 from DuPont, a UVcurable dielectric and an encapsulant, respectively. These inks areflexible and durable and can handle creasing, washing, etc. The degreeof conductivity for different traces and applications is controlled bythe amount or concentration of conductive particles (e.g., silver,copper, aluminum, carbon, etc.) suspended in the silicone. These inkscan be screen printed or printed from an inkjet printer. Another classof implementations uses conductive paints (e.g., carbon particles mixedwith paint) such as those that are commonly used for EMI shielding andESD protection.

Examples of sensors and arrays of sensors that may be used with variousimplementations enabled by the present disclosure are described in U.S.patent application Ser. No. 14/299,976 entitled Piezoresistive Sensorsand Applications filed on Jun. 9, 2014 (Attorney Docket No. BBOPP004),the entire disclosure of which is incorporated herein by reference forall purposes. However, it should be noted that implementations arecontemplated that employ a variety of other suitable sensortechnologies.

Forming sensors on flexible substrates enables numerous useful devices.Many of these devices employ such sensors to detect the occurrence oftouch events, the force or pressure of touch events, the duration oftouch events, the location of touch events, the direction of touchevents, and/or the speed of motion of touch events. The output signalsfrom such sensors may also be used to detect a variety of distortionsand/or deformations of the substrate on which they are formed or withwhich they are integrated such as, for example, bends, stretches,torsions, rotations, etc. The information derived from such sensors maybe used to effect a wide variety of controls and/or effects. Examples ofdistortions and/or deformations are described below with reference tothe accompanying figures. As will be understood, the specific detailsdescribed are merely examples for the purpose of illustrating the rangeof techniques enabled by this disclosure.

FIG. 1 shows an example of a sensor trace pattern 100 integrated with aflexible substrate 102. The flexible substrate may be a piezoresistivematerial or a dielectric material. In the latter case, a flexiblepiezoresistive material is tightly integrated with the dielectricmaterial and in contact with the sensor trace pattern. Trace pattern 100includes a pair of conductive traces, one of which (trace 104) providesa sensor signal to associated circuitry (not shown), and the other ofwhich (trace 106) is connected to ground or a suitable reference. Somerepresentative examples of other trace patterns 108-116 are shown. Insome implementations, the traces of a trace pattern may be formeddirectly, e.g., by screening or printing, on the flexible substratewhich might be, for example, a piezoresistive fabric. However, it shouldbe noted that, among other things, the geometries of the sensor tracepattern(s), the number of traces associated with each sensor, thenumber, spacing, or arrangement of the sensors, the relationship of thesensors to the substrate, the number of layers or substrates, and thenature of the substrate(s) may vary considerably from application toapplication, and that the depicted configurations are merely examplesfor illustrative purposes.

FIG. 2 shows examples of different types of distortions to flexiblesubstrate 102 that may be detected via sensor trace pattern 100. FIG.2(a) shows substrate 102 in its non-distorted state. FIG. 2(b) shows aside view of substrate 102 bending; FIG. 2(c) shows substrate 102stretching; FIG. 2(d) represents substrate 102 rotating relative tosurrounding material; and FIG. 2(e) shows a side view of substrate 102twisting due to an applied torque (i.e., torsion). In each of thesescenarios, the resistance of the piezoresistive material in contact withtrace pattern 100 changes in response to the applied force (e.g., goesdown or up due to compression or increased separation of conductiveparticles in the piezoresistive material). This change (including itsmagnitude and time-varying nature) is detectable via sensor tracepattern 100 and associated electronics (not shown).

According to a particular implementation illustrated in FIG. 3, sensortrace patterns are formed on the stretchable material of a sensor glove300 that may be used, for example, to translate a human's hand motionsand the hand's interactions with the physical world into a virtualrepresentation of the hand (or some other virtual object) and itsinteractions in a virtual environment. In another example, the hand'smotions and interactions may be used to control a robotic hand or devicein the physical world. The material on which the trace patterns areformed may be a flexible piezoresistive material or a flexibledielectric material. Again, in the latter case, a flexiblepiezoresistive material is tightly integrated with the flexiblesubstrate on which the trace patterns are formed and in contact with thetrace patterns at the various sensor locations (i.e., S1-S19).

As shown, trace patterns corresponding to some of the sensors (e.g.,S1-S5 and S14-S18) are placed to coincide with various joints of thefingers (e.g., knuckles or finger joints) to capture distortion and/ordeformation of the glove in response to bending and flexing of thosejoints. Other sensors (e.g., S6-S13 and S19) are placed to capturestretching of the glove, e.g., as occurs when the fingers of the handare spread out. Other sensors (not shown) may also be placed on the palmof the glove and/or the tips of the fingers to detect bending andflexing forces as well as forces relating, for example, to touching,gripping, or otherwise coming into contact with objects or surfaces.

Portions of the conductive traces that are not intended to be part of asensor (e.g., signal routing traces) may be shielded or insulated toreduce any unwanted contributions to the sensor signals. That is, theportions of the conductive traces that bring the drive and sense signalsto and from the sensors may be insulated from the piezoresistivematerial using, for example, a dielectric or non-conducting materialbetween the piezoresistive material and the conductive traces. Accordingto some implementations in which the conductive traces are formed on aflexible dielectric material, isolated pieces of piezoresistive materialmay be selectively located at the respective sensor locations.

In the depicted implementation there are 19 sensors, S1-S19. Each of thesensors includes two adjacent traces, the respective patterns of whichinclude extensions that alternate. See, for example, the magnified viewof sensor S4. One of the traces 301 receives a drive signal; the othertrace 302 transmits the sensor signal to associated sensor circuitry(not shown). The drive signal might be provided, for example, byconnecting the trace (permanently or temporarily) to a voltagereference, a signal source that may include additional information inthe drive signal, a GPIO (General Purpose Input Output) pin of anassociated processor or controller, etc. And as shown in the example inFIG. 3, the sensor signal might be generated using a voltage divider inwhich one of the resistors of the divider includes the resistancebetween the two traces through the intervening piezoresistive material.The other resistor (represented by R1) might be included, for example,with the associated sensor circuitry. As the resistance of thepiezoresistive material changes with applied force or pressure, thesensor signal also varies as a divided portion of the drive signal.

The sensors are energized (via the drive signals) and interrogated (viathe sensor signals) to generate an output signal for each that is arepresentation of the force exerted on that sensor. As will also beappreciated, and depending on the application, implementations arecontemplated having more or fewer sensors.

According to various implementations, different sets of sensors may beselectively energized and interrogated thereby reducing the number andoverall area of traces on the substrate, as well as the requiredconnections to sensor circuitry on an associated PCB (which may bepositioned, for example, in cutout 322). For example, in the sensorsystem of FIG. 3, the 19 sensors are driven via 11 drive signal outputsfrom the sensor circuitry (not shown), and the sensor signals arereceived via 2 sensor signal inputs to the sensor circuitry; with 13connections between the flexible substrate on which the conductivetraces are formed and the PCB in cutout 322 as shown. The set of sensorsproviding sensor signals to one of the 2 sensor signal inputs (e.g.,S6-S13 in one set and S1-S5 and S14-S19 in the other) may be energizedin any suitable sequence or pattern such that any signal received on thecorresponding sensor signal input can be correlated with thecorresponding sensor drive signal by the sensor circuitry.

And because the sensor signals in this implementation are received bythe sensor circuitry via two different sensor signal inputs, two sensorscan be simultaneously energized as long as they are connected todifferent sensor signal inputs to the sensor circuitry. This allows forthe sharing of drive signal lines. For example, in the implementation ofFIG. 3, eight pairs of sensors share a common drive signal line, i.e.,S2 and S8, S3 and S10, S4 and S12, S6 and S14, S7 and S15, S9 and S16,S11 and S17, and S13 and S19. The sharing of the common drive signallines may be enabled by insulators which allow the conductive traces tocross, as well as locations at which the conductive traces simplydiverge. Other suitable variations on this theme will be understood bythose of skill in the art to be within the scope of this disclosure.

According to some implementations, a PCB may be connected to theconductive traces of the sensor array as described U.S. patentapplication Ser. No. 14/671,821 entitled Flexible Sensors andApplications filed on Mar. 27, 2015 (Attorney Docket No. BBOPP004X2),the entire disclosure of which is incorporated herein by reference forall purposes. According to other implementations, any of a variety oftechniques may be employed to make such a connection including, forexample, elastomeric connectors (e.g., ZEBRA® connectors) whichalternate conductive and non-conductive rubber at a density typically anorder of magnitude greater than the width of the conductive traces towhich they connect (e.g., at the edge of the fabric). A variety of othersuitable alternatives are available to those of skill in the art.

FIG. 4 is a simplified diagram of sensor circuitry that may be providedon a PCB for use with implementations described herein. For example, inthe implementation described above with reference to FIG, 3, such sensorcircuitry could be provided on a PCB in cutout 322 and connected to theconductive traces associated with sensors S1-S19. When force is appliedto one of the sensors, a resulting signal (captured via thecorresponding traces) is received and digitized (e.g., via multiplexer402 and A-D converter 404) and may be processed locally (e.g., byprocessor 406) and/or transmitted to a connected device (e.g., via aBluetooth or other wireless connection, or even via a USB connection).The sensors may be selectively energized by the sensor circuitry (e.g.,under the control of processor 406 via D-A converter 408 and multiplexer410) to effect the generation of the sensor signals. The C8051F380-GMcontroller (provided by Silicon Labs of Austin, Tex.) is an example of aprocessor suitable for use with various implementations.

In addition to transmission of data to and from a connected device,power may be provided to the sensor circuitry via a USB connection.Alternatively, systems that transmit data wirelessly (e.g., viaBluetooth) may provide power to the sensor circuitry using any of avariety of mechanisms and techniques including, for example, using oneor more batteries, solar cells, and/or mechanisms that harvestmechanical energy. The LTC3588 (provided by Linear TechnologyCorporation of Milpitas, Calif.) is an example of an energy harvestingpower supply that may be used with at least some of these diverse energysources. Other suitable variations will be appreciated by those of skillin the art. And as will be appreciated, the sensor circuitry shown inFIG. 4 is merely an example. A wide range of sensor circuitrycomponents, configurations, and functionalities are contemplated.

Both one-sided and two-side implementations are contemplated, e.g.,conductive traces can be formed on one or both sides of a flexiblesubstrate. As will be understood, two-sided implementations may requiresome mechanism for connecting conductive traces on one side of thesubstrate to those on the other side. Some implementations use vias inwhich conductive ink or paint is flowed through the vias to establishthe connections. Alternatively or additionally, metal vias or rivets maymake connections through the substrate. FIG. 5 illustrates the use ofvias or rivets through the flexible substrate (e.g., configuration 502),and the use of insulating materials to insulate conductive traces fromthe substrate where the substrate is a piezoresistive material (e.g.,configuration 504). Such mechanisms enable complex patterns of tracesand routing of signals in a manner analogous to the different layers ofa PCB.

For example, assuming an implementation in which the conductive tracesare formed on piezoresistive material and referring again to FIG. 3,conductive traces that transmit signals to and from the sensors of glove300 may be insulated from the underlying piezoresistive substrate by aninsulating material. This is most clearly illustrated in the figure byinsulators 304 and 306 that are associated with the drive and sensesignal lines connected to sensor S4. In addition, sense signal linesfrom multiple sensors are connected to each other on the opposite side(not shown) of the material depicted in FIG. 3 through the use of viasat locations 310-318.

According to a particular implementation of a sensor glove and as shownin FIG. 6, sensor trace patterns (e.g., 601-604) may be placed in aroughly cylindrical configuration around the wrist to detect bending ofthe wrist in two dimensions (e.g., up, down, left, right). When all foursensors register a similar response, this could mean that the wrist istwisting. However, this configuration may not provide sufficientinformation to determine the direction of the twist. Therefore,according to a particular implementation, an outer cylinder 608 may beattached to an inner cylinder 610 with at least two stretch sensors(e.g., 612 and 614). By comparison of the outputs of these stretchsensors, the direction (e.g., 616) as well as the amount of the rotationcan be captured.

FIG. 7 illustrates particular class of implementations of a sensor array700 for use in a sensor glove in which conductive traces are formed on aflexible dielectric substrate 702. Operation of sensor array 700 issimilar to operation of the sensor array of sensor glove 300 asdescribed above. And it should be noted that the depicted configurationof traces might also be included in implementations in which the tracesare formed on piezoresistive material.

According to a particular implementation, substrate 702 may beconstructed from a thermoplastic polyurethane (TPU) material such as,for example, Products 3415 or 3914 from Bemis Associates Inc. ofShirley, Mass. The conductive traces may be screen printed on thesubstrate using a conductive flexible ink such as, for example,conductive silicone-based inks manufactured by E.I. du Pont de Nemoursand Company (DuPont) of Wilmington, Del., or Creative Materials of Ayer,Mass. Patches of a piezoresistive material (e.g., the Eeonyx fabricdiscussed above) are placed in contact with the conductive traces at thelocations of sensors S1-S14. See for example, piezoresistive patch 704at sensor S4. A second substrate of the TPU material (not shown) isplaced over array 700, and the assembly is heated to thermally bond thecomponents together, fixing the piezoresistive patches in contact withtheir respective sensor traces.

The relationships of the components of this assembly may be understoodwith reference to FIG. 8 which shows a flexible substrate 802 on which aconductive trace 804 is formed. Piezoresistive material 806 ismaintained in contact with trace 804 by a second flexible substrate 808.In the depicted example, substrates 802 and 808 are TPU substrates andtrace 804 is a conductive ink that is screen printed on TPU substrate802. According to a particular implementation, TPU substrate 802 has anadhesive-barrier-adhesive (ABA) structure that allows for the assemblyto be thermally bonded (e.g., melted) to another substrate such as, forexample, a fabric glove blank 900 as depicted in FIG. 9. The other TPUsubstrate 808 is shown an adhesive-barrier (AB) structure so that itonly bonds to the assembly. However, implementations are contemplated inwhich this substrate has an ABA structure to enable thermal bonding onboth sides of the assembly.

According to a more specific implementation, stiffeners (not shown) maybe placed in alignment with at least some of the piezoresistive patchesand the corresponding trace patterns for the purpose of amplifying thesignals generated by the corresponding sensors, e.g., by the force ofthe stiffener resisting bending of a knuckle and compressing thepiezoresistive material. A stiffener might be a plastic film (e.g.,polyethylene terephthalate or PET). Alternatively, a stiffener may beanother piece of fabric. As yet another alternative, a stiffeningmaterial such as DuPont 5036 Dielectric ink may be silk-screened orprinted on one of the components of the stack. As will be appreciated,stiffeners may be inserted at any point in the stack of materials (e.g.,as depicted in FIG. 8) as long as the electrical connection between theconductive traces and the piezoresistive material is not undulydegraded.

Referring back to FIG. 7, a stiffener 706 (e.g., of PET or othersuitable material) may be adhered to substrate 702 near the terminationsof the conductive traces to allow for the insertion of the assembly intoa connector 708 (see the exploded view in the lower right hand corner ofthe drawing). As will be appreciated, with stiffener 706 and theappropriate conductor spacing, this configuration allows for connectionof sensor array 700 to any of a wide variety of industry standardconnectors. According to a particular implementation, connector 708 is aMolex ZIF flat flex connector such as, for example, the Molex connector52207-2860 (a 28 position connector) or the Molex connector 0522710869(an 8 position connector as shown in FIG. 11).

As discussed above, sensor glove implementations are contemplated inwhich sensors are placed on the palm of the glove and/or the tips of thefingers to detect, for example, touching, gripping, or otherwise cominginto contact with objects or surfaces. An example of how such a sensormight be integrated with an array is shown in FIG. 10. In the depictedexample, flexible substrate 1002 extends beyond sensor S4 and includes atab 1004 on which the conductive traces of sensor S15 are formed. Tab1004 can be wrapped around inside the glove (as indicated by the arrow)so that it coincides with the fingertip of the glove. Thus, any forcesacting on the fingertip of the glove (e.g., by virtue of the fingertipcoming into contact with a surface) will be detected by sensor S15. Aswill be appreciated, such sensors may be integrated with a sensor arrayfor the back of the hand as shown in FIG. 10. Alternatively, suchsensors may be implemented as separate array for the palm andfingertips.

FIG. 11 shows an alternative design for a sensor array 1100 for use in asensor glove which includes only four elongated sensors; S1-S3 for thethree middle fingers, and S4 for the thumb. As will be appreciated, thissimpler design may be easier and/or cheaper to manufacture and may besufficient or even more well-suited for some applications than thedesigns described above with reference to FIGS. 3 and 7. Nevertheless,sensor array 1100 operates similarly to the sensor arrays described andmay be constructed using either approach. According to a particularimplementation, substrate 1102 is constructed from a TPU material andthe conductive traces are screen printed on substrate 1102 using aconductive flexible ink as described above with reference to FIGS. 7 and8. Patches of a piezoresistive material (e.g., the Eeonyx fabricdiscussed above) are placed in contact with the conductive traces at thelocations of sensors S1-S4. See for example, piezoresistive patch 1104at sensor S3. A second substrate of the TPU material (not shown) isplaced over array 1100, and the assembly is heated to thermally bond thecomponents together, fixing the piezoresistive patches in contact withtheir respective sensor traces.

As with sensor array 700, a stiffener (not shown) may be adhered tosubstrate 1102 near the terminations of the conductive traces to allowfor the insertion of the assembly into a connector 1108. As discussedabove, use of the stiffener allows for connection of sensor array 1100to any of a wide variety of industry standard connectors including, forexample, the Molex connector 0522710869. Also as discussed above withreference to sensor array 700, stiffeners (not shown) may be placed inalignment with at least some of the piezoresistive patches and thecorresponding trace patterns of sensor array 1100 for the purpose ofamplifying the signals generated by the corresponding sensors.

FIGS. 12-14C illustrate another class of implementations for use in asensor glove. Referring to the partially exploded view of FIG. 12,sensor system 1200 includes five digit assemblies 1202 (one for eachfinger or digit of the hand) and four abductor assemblies 1204 (one foreach space between each pair of adjacent digits). These assemblies areconnected to a circuit board 1206 on which is implemented the circuitry(not shown) for energizing and reading signals from the knuckle sensorsand abductor sensors on each assembly. Digit assemblies 1202 areinterconnected via substrate 1208 and abductor assemblies 1204 areinterconnected via substrate 1210. Substrates 1208 and 1210 are securedto opposite sides of circuit board 1206 to form sensor system 1200.Conductors on substrates 1208 and 1210 provide connections betweenconductors on digit assemblies 1202 and abductor assemblies 1204 andcorresponding conductors on circuit board 1206 (not shown). Sensorsystem 1200 is secured by top enclosure 1209 and ergonomic back plate1211 and is aligned with the back of a hand inserted in a sensor glove1300 as illustrated in FIG. 13.

Each digit assembly 1202 includes two knuckle sensors, each knucklesensor being formed using a strip of piezoresistive material 1212 (e.g.,a fabric) in contact with a group of sensor traces (obscured by material1212 in FIG. 12) on the surface of a flexible dielectric substrate 1214.Routing traces 1216 by which signals are transmitted to and receivedfrom the individual sensors are adjacent the opposite surface ofsubstrate 1214 from the sensor trace groups (i.e., the underside ofsubstrate 1214 in the figure). Routing traces 1216 are connected to thesensor traces through substrate 1214, e.g., using vias. Substrate 1214is depicted as being transparent so that routing traces 1216 on itsunderside are at least partially visible. Each knuckle sensor generatesa sensor signal that represents the degree of bend in the correspondingknuckle.

Each abductor assembly 1204 includes one abductor sensor formed using astrip of piezoresistive material 1218 (only one of which is shown inFIG. 12), e.g., a fabric, in contact with a group of sensor traces 1219(one set of which is obscured by material 1218) on the surface of aflexible dielectric substrate 1220. Routing traces (not shown) by whichsignals are transmitted to and received from the abductor sensor areadjacent the opposite surface of substrate 1220 from the sensor tracegroup (i.e., the underside of substrate 1220 in the figure). The routingtraces are connected to sensor traces 1219 through substrate 1220, e.g.,using vias. Each abductor sensor generates a sensor signal thatrepresents the spread angle between two adjacent digits. The orientationof sensor system 1200 within a glove may be understood with reference toFIG. 13.

As shown in FIG. 13, each digit assembly 1302 extends along the back ofthe glove and along one of the corresponding fingers (referring to thethumb as one of the fingers). As a particular finger bends, the degreeof bend of its knuckles are represented by the sensor signals generatedby the corresponding knuckle sensors. And as will be understood from thefigure, when the fingers of the hand are together, the portion of eachabductor assembly 1304 including the abductor sensor is bent back onitself almost 180 degrees (e.g., like a taco shell or a “v”) with thecenter line of the bend being aligned with the crux of the twocorresponding adjacent digits. The abductor sensor is considered to be“at rest” in this position. As the fingers are spread apart, theabductor sensor flattens out and stretches, generating a correspondingsensor signal representing the spread angle.

The individual sensors on the digit and abductor assemblies may beenergized and interrogated as described above with reference to FIG. 3using sensor circuitry such as that described with reference to FIG. 4.That is, each of the sensors includes two traces. One of the tracesreceives a drive signal, and the other transmits the sensor signal tothe sensor circuitry. As discussed above, the sensor signal may begenerated using a voltage divider in which one of the resistors of thedivider includes the resistance between the two traces through theintervening piezoresistive material, and the other is included with thesensor circuitry. As the resistance of the piezoresistive materialchanges with applied force or pressure, the sensor signal also varies asa divided portion of the drive signal.

And as will be understood, the responses of the individual sensors insensor systems enabled by the present disclosure may exhibit variationrelative to each other as well as the corresponding sensors in similarsystems. According to some implementations, calibrated sensor data arestored (e.g., in memory 407 of processor 406) that represent theresponse of each of the sensors. Such data ensure consistency andaccuracy in the way the sensor outputs are processed and used torepresent the motion and articulation of the parts of the hand. Duringcalibration, the output of each sensor (e.g., as captured by ADC 404) ismeasured for a range of known input forces corresponding to specificpositions of the hand. In this way, a set of data points for each sensoris captured (e.g., in a table in memory 407) associating ADC values withcorresponding finger positions. The data set for each sensor may capturea value (or an offset value) for many (or even every) of the possiblevalues of the ADC output. Alternatively, fewer data points may becaptured and the sensor circuitry may use interpolation to derive forcevalues for ADC outputs not represented in the data set.

The calibration data for each abductor sensor represent a range of thespread of the corresponding pair of fingers with a range of data values.The calibration data for each knuckle sensor represent a range of thebend of the corresponding knuckle with a range of data values. Accordingto a particular implementation, calibration involves holding the hand invarious positions and storing data values for those positions. Forexample, the user might be instructed (e.g., in a video or animation) tohold her hand out relaxed with the fingers together, make a fist, spreadthe fingers out, etc. Data values for each sensor may then be capturedfor each position.

According to a particular implementation, the calibration data capturetwo positions of the range for each sensor. These positions may be, forexample, at the extreme ends of each range. For example, for an abductorsensor, the two positions might be (1) the pair of fingers together and(2) the pair of fingers spread apart as far as possible. Similarly, fora knuckle sensor, the two positions might be (1) the knuckle straightand (2) the knuckle bent as far as possible. Interpolation (e.g., linearinterpolation) is then used at run time to determine positions in therange between the extremes for each knuckle and abductor sensor. Thesecalibration data can be stored across sessions. And because such datacan be user-specific, this might include the storing of multiple sets;one for each unique user. Alternatively, the calibration data can beregenerated for each session, e.g., by running the user through thevarious hand positions of the calibration routine.

According to some implementations, the sensor circuitry on circuit board1206 includes an inertial measurement unit (IMU) (not shown) thatincludes a 3-axis accelerometer, a 3-axis gyroscope, and a 3-axismagnetometer. The information from these components is blended by theIMU to give the attitude of the hand, i.e., pitch, roll, and yaw.Translation, i.e., movement of the hand in x, y, and z, may be trackedusing one or more cameras (e.g., gaming system cameras), one or moreultrasonic sensors, one or more electromagnetic sensors, etc., todetermine the position of the glove in space. Thus, using theinformation generated by the sensor system, the IMU, and any translationsensing system, the position, attitude, and finger articulations of theuser's hand can be captured. An example of an IMU that may be employedwith various implementations is the BNO055 provided by Bosch SensortecGmbH of Reutlingen/Kusterdingen, Germany. Other examples of suitableIMUs are provided by InvenSense, Inc. of San Jose, Calif., and STMicroelectronics of Geneva, Switzerland.

In the implementation depicted in FIG. 12, each digit assembly alsoincludes a haptic actuator (not shown for clarity) which is connected toits own set of routing traces (partially visible) via pads 1224. Thehaptic actuators are aligned with each fingertip for the purpose ofcreating the sensation that the fingertip is in contact with an objector a surface (e.g., in a virtual space or at a remote location) therebygiving the user a sense of feel. Because sensor system 1200 is alignedwith the back of the hand, the haptic actuators are connected to pads1224 via conductors (not shown) that wrap around the finger.

According to a particular implementation, each actuator is a flexiblemetal membrane (e.g., a kapton-mylar film) stretched over a rigidsubstrate. The membrane shrinks or expands based on a voltage applied bythe sensor circuitry via pads 1224. The haptic actuators can be thoughtof as tiny “speakers” that are driven with different waveforms tosimulate different surfaces, signaling that the fingers have contactedsomething in the virtual world or at the remote location. The waveformsfor these contact events depend on the nature of the surface beingsimulated, the number of fingertips contacting the surface, the rate ofmovement across the virtual surface, etc. In some cases, accompanyingaudio may be provided to enhance the perception of the contact. Examplesof haptic actuators that may be used with various implementationsinclude those provided by Novasentis Inc. of Berkeley, Calif.

FIGS. 14A-14C show a stack of components of a sensor system thatincludes the knuckle sensors and haptic actuators. The componentsrelating to the abductor sensors are not shown for clarity. However, itwill be understood that the abductor assemblies may be formed similarlyto the depicted digit assemblies in terms of the materials and theordering of the components (without the components relating to thehaptic actuators).

Referring to FIG. 14A, ergonomic back plate 1402 is shown at the bottomof the stack relative to the orientation of the figure. Back plate 1402has a curved surface that conforms to the back of the user's hand.Haptic bus lines 1404 (for connection to the haptic actuators which arenot shown) are printed with conductive ink on one side of PET substrate1406. Sensor bus lines 1408 (including pads for connection to the sensorcircuitry circuit board) that are used to energize and read signals fromeach of the knuckle sensors are printed with conductive ink on the otherside of PET substrate 1406.

Referring to FIG. 14B, PET substrates 1410 are placed over sensor buslines 1408 and PET substrate 1406. Sensor traces 1412 (including sometraces to connect to the bus lines) are printed in conductive ink on PETsubstrates 1410 (and partially on PET substrate 1406 to connect with buslines 1408). Each parallel pair of traces (e.g., 1413) on PET substrates1410 corresponds to a knuckle sensor. A carbon passivation layer 1414 isprinted over sensor traces 1412, and exposed portions of bus lines 1408to protect the conductive traces from tarnishing and creeping.Dielectric strips may be placed over portions of the bus traces toinsulate them from the sensor traces and the piezoresistive material.

Referring to FIG. 14C, piezoresistive fabric strips 1416 are placed incontact with each pair of sensor traces 1412 to form the knucklesensors. Each fabric strip 1416 has a PET strip 1418 applied as astiffener that is secured using pressure sensitive adhesive (PSA) 1420.PET 1418 makes fabric 1416 asymmetrically stiffer, resisting the bend ofthe fabric, causing it to distort, thereby enhancing the bend signal andhelping to achieve the desired sensor response and dynamic range. Aswill be appreciated, a variety of materials of varying stiffness and/orthickness can be used as stiffeners depending on the desired responseand dynamic range. TPU strips 1422 are placed over the knuckle sensorsand heated to thermally bond the components together, fixing thepiezoresistive strips in contact with their respective sensor traces.

As mentioned above, sensor traces 1412 are printed such that portions ofthe sensor traces are on PET substrates 1410 and other portions arecontacting and connecting with bus lines 1408 on the underlying PETsubstrate 1406. Connections between sensor traces 1412 and bus lines1408 may also be made through PET substrate 1406, e.g., using vias. Andalthough the knuckle sensors are depicted as using two parallel tracesother trace group configurations are contemplated. For example, sensortraces having interdigitated extensions are employed with someimplementations as discussed above. Another example of such animplementation is shown in FIGS. 15 and 16.

FIG. 15 shows the sensor traces and bus lines of a sensor system 1500without other layers and components so as not to obscure details ofthese structures. Each of the five digit assemblies 1502 includes fourknuckle sensors 1504 as indicated on the digit assembly corresponding tothe middle finger. Having two sensors per knuckle may allow for finerdetection and/or representation of motion. Four abductor assemblies 1506are also shown.

According to this class of implementations and as depicted in FIG. 16,bus lines 1602 (which include both sensor and haptic bus lines) areprinted in conductive ink on one side of a TPU substrate 1604. Sensortraces 1606 are printed in conductive ink on the other side of TPUsubstrate 1604 and connected to the corresponding bus lines through TPUsubstrate 1604, e.g., using vias. This assembly is then placed incontact with piezoresistive fabric, e.g., in the shape of a glove blank(not shown). These components are then heated, securing the sensortraces 1606 to the piezoresistive fabric from which a sensor glove isthen made. Abductor assemblies 1608 (of which only the traces are shown)may be similarly constructed. Alternatively, because of their relativelysimple structures, abductor assemblies 1608 may be formed on thepiezoresistive fabric, e.g., printed using conductive ink and insulators(for the bus lines extending to and from the abductor sensors).

As should be appreciated with reference to the foregoing description,the applications for sensor gloves enabled by the present disclosure arenumerous and diverse. As mentioned above, the action of a human hand insuch a sensor glove may be translated to control systems, devices, andprocesses in both the real and virtual worlds. Using a sensor glove, ahuman can interact with objects in a virtual space, having utility invideo and online gaming, as well as educational and artisticapplications. For example, a sensor glove may be used to simulate asurgical procedure, playing of a virtual musical instrument, conductingof a virtual orchestra, painting of a virtual work of art, etc.Translation of the movements of a human hand into the virtual worldcould support more realistic computer aided animation. Industrialapplications might include remote control of manufacturing apparatus orrobotics handling hazardous materials. As will be appreciated from thediversity of these examples, the range of applications is virtuallylimitless. The scope of this disclosure should therefore not be limitedby reference to specific applications.

It will be understood by those skilled in the art that changes in theform and details of the implementations described herein may be madewithout departing from the scope of this disclosure. In addition,although various advantages and aspects may have been described withreference to particular implementations, the scope of this disclosureshould not be limited by reference to such advantages and aspects.

What is claimed is:
 1. A sensor array, comprising: a first thermoplasticpolyurethane (TPU) substrate; a plurality of conductive traces on thefirst TPU substrate, the conductive traces including a plurality ofsensor traces and a plurality of signal routing traces; andpiezoresistive fabric thermally bonded to the first TPU substrate and incontact with the sensor traces, the piezoresistive fabric and the sensortraces forming a plurality of sensors.
 2. The sensor array of claim 1,wherein the piezoresistive fabric comprises a plurality of patches, eachof the patches being associated with one of the sensors.
 3. The sensorarray of claim 1, further comprising a second TPU substrate thermallybonded to the first TPU substrate and the piezoresistive fabric, therebyenclosing the plurality of sensors between the first and second TPUsubstrates.
 4. The sensor array of claim 3, wherein one or both of thefirst and second TPU substrates is characterized by anadhesive-barrier-adhesive structure such that the sensor array isconfigured to be thermally bonded to an additional substrate.
 5. Thesensor array of claim 1, wherein the conductive traces comprise aconductive flexible ink printed on the first TPU substrate.
 6. Thesensor array of claim 1, wherein the sensor traces are on a firstsurface of the first TPU substrate facing toward the piezoresistivefabric, and wherein at least some of the signal routing traces are on asecond surface of the first TPU substrate facing away from thepiezoresistive fabric.
 7. The sensor array of claim 1, furthercomprising sensor circuitry configured to selectively activate thesensors via first signal routing traces, and to receive sensor signalsfrom the sensors via second signal routing traces.
 8. The sensor arrayof claim 7, wherein the sensor circuitry is further configured toprocess the sensor signals to detect one or more of mechanical force onthe piezoresistive fabric, pressure on the piezoresistive fabric,distortion of the piezoresistive fabric, or deformation of thepiezoresistive fabric.
 9. The sensor array of claim 7, wherein thesensor circuitry is further configured to process the sensor signals todetermine a speed and a direction of motion of an object in contact witha surface of the sensor array.
 10. The sensor array of claim 7, whereinthe sensor circuitry is further configured to generate force data usingthe sensor signals and stored sensor data that represent a response ofeach of the sensors.
 11. The sensor array of claim 10, wherein thesensor circuitry includes an analog-to-digital converter (ADC)configured to convert the sensor signals to corresponding digitalsignals, and wherein the stored sensor data for each sensor represent adata point for each possible value of the corresponding digital signal.12. The sensor array of claim 10, wherein the sensor circuitry includesan analog-to-digital converter (ADC) configured to convert the sensorsignals to corresponding digital signals, wherein the stored sensor datafor each sensor represent a data point for fewer than all of thepossible values of the corresponding digital signal, and wherein thesensor circuitry is configured to generate the force data for eachsensor by interpolating between the data points stored for that sensor.13. The sensor array of claim 7, wherein a first sensor of the pluralityof sensors includes a portion of the piezoresistive fabric, a firstsensor trace of the plurality of sensor traces, and a second sensortrace of the plurality of sensor traces, the portion of thepiezoresistive fabric, the first sensor trace, and the second sensortrace forming part of a voltage divider configured to generate acorresponding one of the sensor signals.
 14. The sensor array of claim1, further comprising a plurality of stiffeners, each stiffener beingaligned with at least one of the sensors.
 15. The sensor array of claim1, further comprising an insulating material formed over a firstconductive trace, thereby allowing a second conductive trace to crossthe first conductive trace.
 16. A method for fabricating a sensor array,comprising: forming a plurality of conductive sensor traces on a firstthermoplastic polyurethane (TPU) substrate; forming a plurality ofconductive signal routing traces on the first TPU substrate; placingpiezoresistive fabric adjacent the first TPU substrate; and thermallybonding the piezoresistive fabric to the first TPU substrate such thatthe piezoresistive fabric is secured in contact with the sensor traces,the piezoresistive fabric and the sensor traces forming a plurality ofsensors.
 17. The method of claim 16, wherein the piezoresistive fabriccomprises a plurality of patches, and wherein placing the piezoresistivefabric adjacent the TPU substrate comprises aligning each of the patcheswith a corresponding set of the sensor traces.
 18. The method of claim16, further comprising: placing a second TPU substrate adjacent thefirst TPU substrate and the piezoresistive fabric; and thermally bondingthe second TPU substrate to the first TPU substrate and thepiezoresistive fabric, thereby enclosing the plurality of sensorsbetween the first and second TPU substrates.
 19. The method of claim 18,wherein one or both of the first and second TPU substrates ischaracterized by an adhesive-barrier-adhesive structure, the methodfurther comprising thermally bonding the sensor array to an additionalsubstrate.
 20. The method of claim 16, wherein forming the sensor tracesand the signal routing traces on the first TPU substrate comprisesprinting the sensor traces and the signal routing traces on the firstTPU substrate using a conductive flexible ink.
 21. The method of claim16, wherein forming the sensor traces and the signal routing traces onthe first TPU substrate comprises: forming the sensor traces on a firstsurface of the first TPU substrate that faces toward the piezoresistivefabric; and forming at least some of the signal routing traces on asecond surface of the first TPU substrate that faces away from thepiezoresistive fabric.
 22. The method of claim 21, further comprisingconnecting the sensor traces to corresponding signal routing tracesthrough the TPU substrate.
 23. The method of claim 16, furthercomprising: selectively activating the sensors via first signal routingtraces; receiving sensor signals from the sensors via second signalrouting traces; and for each of the sensors: applying a range of knownforces to the sensor; generating force data for the sensor based on acorresponding one of the sensor signals, the force data representing aresponse of the sensor to the range of known forces; and storing sensordata for the sensor, the sensor data representing a plurality of datapoints that correlate the force data with the range of known forces. 24.The method of claim 23, wherein the sensor data for each sensorrepresent a data point for each possible value of the correspondingforce data, or wherein the sensor data for each sensor represent a datapoint for fewer than all of the possible values of the correspondingforce data.
 25. The method of claim 16, further comprising integrating aplurality of stiffeners with the sensor array, each stiffener beingaligned with at least one of the sensors.
 26. The method of claim 16,wherein forming the sensor traces and the signal routing traces on thefirst TPU substrate comprises: forming an insulating material over afirst conductive trace; and forming a second conductive trace over theinsulating material, thereby allowing the second conductive trace tocross the first conductive trace.
 27. A sensor, comprising: a firstthermoplastic polyurethane (TPU) substrate; a plurality of conductivetraces on the first TPU substrate, the conductive traces including twoor more sensor traces and two or more signal routing traces; andpiezoresistive fabric thermally bonded to the first TPU substrate and incontact with the sensor traces, the piezoresistive fabric and the sensortraces forming the sensor.
 28. The sensor of claim 27, furthercomprising a second TPU substrate thermally bonded to the first TPUsubstrate and the piezoresistive fabric, thereby enclosing the sensorbetween the first and second TPU substrates.
 29. The sensor of claim 28,wherein one or both of the first and second TPU substrates ischaracterized by an adhesive-barrier-adhesive structure such that thesensor is configured to be thermally bonded to an additional substrate.30. The sensor of claim 27, wherein the conductive traces comprise aconductive flexible ink printed on the first TPU substrate.
 31. Thesensor of claim 27, further comprising sensor circuitry configured toactivate the sensor via a first signal routing trace, and to receive asensor signal from the sensor via a second signal routing trace, thesensor circuitry being further configured to process the sensor signalto detect one or more of mechanical force on the piezoresistive fabric,pressure on the piezoresistive fabric, distortion of the piezoresistivefabric, or deformation of the piezoresistive fabric.
 32. The sensor ofclaim 31, wherein the sensor circuitry is further configured to generateforce data using the sensor signals and stored sensor data thatrepresent a response of the sensor.
 33. The sensor of claim 32, whereinthe sensor circuitry includes an analog-to-digital converter (ADC)configured to convert the sensor signal to a digital signal, and whereinthe stored sensor data for the sensor represent a data point for eachpossible value of the digital signal.
 34. The sensor of claim 32,wherein the sensor circuitry includes an analog-to-digital converter(ADC) configured to convert the sensor signal to a digital signal,wherein the stored sensor data for each sensor represent a data pointfor fewer than all of the possible values of the digital signal, andwherein the sensor circuitry is configured to generate the force datafor the sensor by interpolating between the data points.
 35. The sensorof claim 31, wherein the piezoresistive fabric and the sensors traceform part of a voltage divider configured to generate the sensor signal.36. The sensor of claim 27, further comprising a stiffener aligned withthe sensor.